I. Field of the Invention
The present invention relates generally to turbine engine constructions and, more particularly, to a turbine engine construction with means for cooling the turbine shrouds and also to minimize hot air leakage around the first turbine stage.
II. Description of the Prior Art
Turbine engines typically comprise a support housing having a compressor and one or more turbine stages secured to a turbine shaft rotatably mounted in the support housing. The turbine compressor supplies compressed air to a combustor into which fuel is also injected and ignited. The hot and expanding gases resulting from combustion in the combustor exhausts through a turbine nozzle and through the turbine stage or stages to rotatably drive both the turbine stages and the turbine compressor via the turbine shaft.
In one type of previously known turbine engine construction, an annular rotating shroud is attached to the outer periphery of the turbine blades forming the first turbine stage while a cooperating static shroud is attached to or formed as a part of the support housing coaxially around and spaced radially outwardly from the rotating shroud. One or more labyrinth seals are oftentimes positioned between the static and rotating shrouds to reduce the leakage of hot gases through the shroud clearance space but such seals are only capable of reducing, not eliminating, such leakage. The leakage of hot gases through the shroud clearance space results in both a pressure energy loss and thermal energy loss since no useful work is performed by the leakage air flow.
A number of previously known turbine engine constructions also employ cooling means for cooling the outer or static shroud in order to minimize its thermal expansion during operation of the turbine engine. For example, it is well known to divert a portion of the relatively cool air from the compressor outlet across the radial outer surface of the static shroud. While reduction of the thermal expansion of the static shroud improves the overall efficiency of the turbine engine by reducing the shroud clearance space, some leakage still occurs.
These previously known turbine engines with static shroud cooling means, however, are ineffective in cooling the rotating shroud on the turbine rotor so that the rotating shroud rapidly attains the gas temperature of the turbine exhaust gases. The stress rupture life of the rotating shroud thus limits the inlet temperature into the turbine stages and, hence, the overall turbine engine efficiency.